Positional information acquisition device, positional information acquisition method, positional information acquisition program, and radiography apparatus

ABSTRACT

An image acquisition unit acquires a radiographic image set including a plurality of radiographic images, which have been generated by alternately irradiating a subject with radiation emitted from a plurality of radiation sources provided at different positions and alternately detecting the radiation transmitted through the subject using one detection unit, at a predetermined time interval. A feature point detection unit detects at least one common feature point in the subject from each of the plurality of radiographic images included in the radiographic image set. A positional information derivation unit derives three-dimensional positional information of the at least one feature point in the subject using a positional relationship between a position of the at least one feature point detected from each of the plurality of radiographic images on a detection surface of the detection unit and positions of the plurality of radiation sources.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2019-060368 filed on Mar. 27, 2019. Theabove application is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND Technical Field

The present disclosure relates to a positional information acquisitiondevice, a positional information acquisition method, a positionalinformation acquisition program, and a radiography apparatus thatacquire three-dimensional positional information of a feature point in asubject.

Related Art

In surgical operations and catheter treatments, it is necessary tounderstand the positional relationship between surgical instruments andhuman body structure such as bones and blood vessels. However, in therelated art, in many cases, the understanding of the positionalrelationship between a surgical instrument and a human body structuredepends on the experience and intuition of a doctor and there areproblems of an error in the insertion of the surgical instrument andexcessive surgery time. For this reason, a process is performed whichcaptures an image of a subject using a radioscopy apparatus duringsurgery and understands the positional relationship between a surgicalinstrument and a human body structure using a radioscopic imagedisplayed on a display by imaging. However, while a three-dimensionalpositional relationship is established between the surgical instrumentand the human body structure, the radioscopic image is a two-dimensionalimage. It is difficult for the user to understand the three-dimensionalpositional relationship between the surgical instrument and the humanbody structure even in a case in which the user views thetwo-dimensional radioscopic image.

For this reason, a process is performed which understands athree-dimensional positional relationship between a surgical instrumentand a human body structure, using radioscopic images in a plurality ofdirections acquired by capturing the images of a patient as a subjectwhile changing an angle during a medical procedure or by using aplurality of imaging apparatuses at the same time. In addition, a methodhas been proposed in which a sensor is attached to a surgical instrumentto understand the three-dimensional position of the surgical instrument.

However, in a case in which an image of a subject is captured while theangle is changed, it is necessary to move the imaging apparatus during amedical procedure. In addition, in a case in which a plurality ofimaging apparatuses are used at the same time, it is not necessary tomove the imaging apparatuses, but a work space for the doctor duringsurgery is reduced, which may hinder the procedure. Further, in themethod using a sensor, it is necessary to prepare a sensor.

For this reason, a method has been proposed which acquires a pluralityof radiographic images obtained by irradiating a subject with radiationemitted from a plurality of radiation sources arranged at intervals tocapture the images of the subject at a plurality of positions andgenerates a three-dimensional radiographic image, in which the subjectcan be viewed stereoscopically, from the plurality of radiographicimages (for example, see JP2014-226174A). According to the methoddisclosed in JP2014-226174A, the doctor stereoscopically views thethree-dimensional radiographic image to understand a three-dimensionalpositional relationship between a surgical instrument and a human bodystructure.

In surgical operations and catheter treatments, it is necessary tounderstand the positional relationship between a surgical instrument anda human body structure in real time. However, in the method described inJP2014-226174A, the processing time for generating a three-dimensionalradiographic image is required. In recent years, since the resolutionand density resolution of radiographic images have improved, the amountof image data indicating a radiographic image has become very large.Time is required for a process to generate a three-dimensional imagefrom the radiographic images having a large amount of data. For thisreason, in the method described in JP2014-226174A, it is difficult tounderstand the position between the surgical instrument and the humanbody structure in the subject and the positional relationshiptherebetween in real time.

SUMMARY OF THE INVENTION

The present disclosure has been made in view of the above-mentionedproblems and an object of the present disclosure is to provide atechnique that enables a user to understand a three-dimensional positionof a feature point, such as a surgical instrument, in a subject in realtime.

According to the present disclosure, there is provided a positionalinformation acquisition device comprising: an image acquisition unitthat acquires a radiographic image set including a plurality ofradiographic images, which have been generated by alternatelyirradiating a subject with radiation emitted from a plurality ofradiation sources provided at different positions and alternatelydetecting the radiation transmitted through the subject using onedetection unit, at a predetermined time interval; a feature pointdetection unit that detects at least one common feature point in thesubject from each of the plurality of radiographic images included inthe radiographic image set; and a positional information derivation unitthat derives three-dimensional positional information of the at leastone feature point in the subject using a positional relationship betweena position of the at least one feature point detected from each of theplurality of radiographic images on a detection surface of the detectionunit and positions of the plurality of radiation sources.

The “predetermined time interval” means, for example, a time intervalcorresponding to the frame rate of a moving image. The predeterminedtime interval may be, for example, 25 to 60 fps. As a result, in thepresent disclosure, a combination of radiographic images, such as amoving image, is acquired. In addition, all of the plurality ofradiographic images may be acquired at the same time interval or theplurality of radiographic images may be acquired at different timeintervals.

The positional information acquisition device according to the presentdisclosure may further comprise a display control unit that displays thepositional information on a display unit.

In the positional information acquisition device according to thepresent disclosure, the feature point detection unit may detect a pointon a surgical instrument inserted into the subject as the feature point.

According to the present disclosure, there is provided a radiographyapparatus comprising: a plurality of radiation sources that are providedat a predetermined interval; a detection unit that is provided so as toface the plurality of radiation sources, detects radiation which hasbeen emitted from each of the plurality of radiation sources andtransmitted through a subject, and generates a radiographic image of thesubject; an imaging control unit that generates a radiographic image setincluding a plurality of radiographic images at a predetermined timeinterval by controlling a timing when each of the plurality of radiationsources emits the radiation and a timing when the detection unit detectsthe radiation transmitted through the subject such that the plurality ofradiation sources alternately irradiate the subject with the radiationand the detection unit alternately detects the radiation transmittedthrough the subject; and the positional information acquisition deviceaccording to the present disclosure.

In the radiography apparatus according to the present disclosure, thenumber of radiation sources may be 2.

In the radiography apparatus according to the present disclosure, theimaging control unit may direct one of the two radiation sources tosequentially emit radiation at a first time interval, direct the otherradiation source to sequentially emit radiation at a second timeinterval equal to or longer than the first time interval, and controlthe detection unit so as to detect the radiation at all timings when thetwo radiation sources emit the radiation. The image acquisition unit mayacquire, as the radiographic image set, two radiographic imagesgenerated by detecting two temporally adjacent radiations which havebeen emitted from the two radiation sources using the detection unit.

The term “being equal to or longer than the first time interval” meansbeing equal to the first time interval and being longer than the firsttime interval.

According to the present disclosure, there is provided a positionalinformation acquisition method comprising: acquiring a radiographicimage set including a plurality of radiographic images, which have beengenerated by alternately irradiating a subject with radiation emittedfrom a plurality of radiation sources provided at different positionsand alternately detecting the radiation transmitted through the subjectusing one detection unit, at a predetermined time interval; detecting atleast one common feature point in the subject from each of the pluralityof radiographic images included in the radiographic image set; andderiving three-dimensional positional information of the at least onefeature point in the subject using a positional relationship between aposition of the at least one feature point detected from each of theplurality of radiographic images on a detection surface of the detectionunit and positions of the plurality of radiation sources.

In addition, a program that causes a computer to perform the positionalinformation acquisition method according to the present disclosure maybe provided.

According to the present disclosure, there is provided anotherpositional information acquisition device comprising a memory thatstores commands to be executed by a computer and a processor that isconfigured to execute the stored commands. The processor performs aprocess of acquiring a radiographic image set including a plurality ofradiographic images, which have been generated by alternatelyirradiating a subject with radiation emitted from a plurality ofradiation sources provided at different positions and alternatelydetecting the radiation transmitted through the subject using onedetection unit, at a predetermined time interval, a process of detectingat least one common feature point in the subject from each of theplurality of radiographic images included in the radiographic image set,and a process of deriving three-dimensional positional information ofthe at least one feature point in the subject using a positionalrelationship between a position of the at least one feature pointdetected from each of the plurality of radiographic images on adetection surface of the detection unit and positions of the pluralityof radiation sources.

According to the present disclosure, it is possible to understand theposition of feature points, such as a surgical instrument and a humanbody structure, in the subject in real time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating the configuration of aradiography apparatus to which a positional information acquisitiondevice according to an embodiment of the present disclosure is applied.

FIG. 2 is a diagram schematically illustrating the configuration of aradiation emitting unit.

FIG. 3 is a diagram schematically illustrating the configuration of thepositional information acquisition device implemented by installing apositional information acquisition program in a computer in thisembodiment.

FIG. 4 is a diagram illustrating the timing when first and secondradiation sources emit radiation and the timing when a radiationdetector detects radiation.

FIG. 5 is a diagram illustrating a radioscopic image displayed in a casein which a catheter treatment is performed.

FIG. 6 is a diagram illustrating a state in which there is a differencebetween the positions of a stent and a guide wire.

FIG. 7 is a diagram illustrating lumbar spine fusion.

FIG. 8 is a diagram illustrating the derivation of three-dimensionalpositional information of a feature point.

FIG. 9 is a diagram illustrating imaging in two directions.

FIG. 10 is a diagram illustrating radiographic images acquired byimaging in two directions.

FIG. 11 is a diagram illustrating projection images in two directionsgenerated from a three-dimensional image.

FIG. 12 is a diagram illustrating radiographic images acquired byimaging in two directions.

FIG. 13 is a diagram illustrating a positional information screen in thecase of a catheter treatment.

FIG. 14 is a diagram illustrating a positional information screen in thecase of lumbar spine fusion.

FIG. 15 is a flowchart illustrating a process performed in thisembodiment.

FIG. 16 is a diagram illustrating the timing when the first and secondradiation sources emit radiation and the timing when the radiationdetector detects radiation.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present disclosure will be describedwith reference to the drawings. FIG. 1 is a diagram schematicallyillustrating the configuration of a radiography apparatus to which apositional information acquisition device according to the embodiment ofthe present disclosure is applied. The radiography apparatus accordingto this embodiment acquires and displays a radioscopic image of asubject H as a moving image in a case in which, for example, a surgicaloperation and a catheter treatment are performed on the subject H.

In this embodiment, it is assumed that the x-axis is set as theleft-right direction of FIG. 1, the y-axis is set as the depth directionof FIG. 1, and the z-axis is set as a direction perpendicular to theplane on which the radiography apparatus 1 illustrated in FIG. 1 isplaced.

As illustrated in FIG. 1, the radiography apparatus 1 according to thisembodiment comprises a C-arm 2. An imaging unit 3 is attached to one endportion of the C-arm 2 and a radiation emitting unit 4 is attached tothe other end portion so as to face the imaging unit 3.

A radiation detector 5, such as a flat panel detector, is provided inthe imaging unit 3. The radiation detector 5 corresponds to a detectionunit according to the present disclosure. In addition, for example, acircuit substrate provided with a charge amplifier that converts acharge signal read from the radiation detector 5 into a voltage signal,a correlated double sampling circuit that samples the voltage signaloutput from the charge amplifier, an analog-to-digital (AD) conversionunit that converts the voltage signal into a digital signal, and thelike is provided in the imaging unit 3. In this embodiment, theradiation detector 5 is used. However, the detector is not limited tothe radiation detector 5 as long as it can detect radiation and convertthe radiation into an image. For example, a detection device, such as animage intensifier, may be used.

The radiation detector 5 can repeatedly perform the recording andreading of a radiographic image and may be a so-called direct-typeradiation detector that directly converts radiation, such as X-rays,into charge or a so-called indirect-type radiation detector thatconverts radiation into visible light and then converts the visiblelight into a charge signal. In addition, it is preferable that aso-called TFT reading method which turns on and off a thin filmtransistor (TFT) switch to read a radiographic image signal or aso-called optical reading method which emits reading light to read aradiographic image signal is used as a radiographic image signal readingmethod. However, the invention is not limited thereto and other readingmethods may be used.

FIG. 2 is a diagram schematically illustrating the configuration of theradiation emitting unit 4. As illustrated in FIG. 2, a first radiationsource 6A and a second radiation source 6B are provided in the radiationemitting unit 4. The first and second radiation sources 6A and 6B arearranged side by side at a predetermined interval in the depth direction(that is, the y-axis direction) of FIG. 1. First and second radiationsR1 and R2 emitted from the first and second radiation sources 6A and 6Bare emitted to the imaging unit 3 through first and second emissionportions 4A and 4B, respectively.

The first and second radiation sources 6A and 6B emit X-rays asradiation and an imaging control unit 14 which will be described belowcontrols the timing when the first and second radiation sources 6A and6B emit radiation and the timing when the radiation detector 5 detectsthe first and second radiations R1 and R2. In addition, for example, theimaging control unit 14 controls the radiation generation conditions ofthe first and second radiation sources 6A and 6B, that is, the selectionof a target and a filter material, a tube voltage, and an irradiationtime.

In the radiography apparatus 1 according to this embodiment, a so-calledsource image distance (SID) which is a distance between a detectionsurface 5A of the radiation detector 5 and the first and secondradiation sources 6A and 6B of the radiation emitting unit 4 is a fixedvalue.

The C-arm 2 according to this embodiment is held by a C-arm holdingportion 7 such that the C-arm 2 can be moved in the direction of anarrow A illustrated in FIG. 1 and the angle of the imaging unit 3 andthe radiation emitting unit 4 with respect to the z direction (verticaldirection) illustrated in FIG. 1 can be integrally changed. Further, theC-arm holding portion 7 has a shaft portion 8 and the shaft portion 8connects the C-arm 2 to a bearing 9 so as to be rotatable. Therefore,the C-arm 2 is rotatable on the shaft portion 8 as a rotation axis inthe direction of an arrow B illustrated in FIG. 1.

In addition, as illustrated in FIG. 1, the radiography apparatus 1according to this embodiment comprises a main body unit 10. The mainbody unit 10 has a plurality of wheels 11 attached to the bottom.Therefore, the radiography apparatus 1 according to this embodiment canbe moved. A support shaft 12 that expands and contracts in the z-axisdirection of FIG. 1 is provided in an upper part of a housing of themain body unit 10 in FIG. 1. The bearing 9 is held above the supportshaft 12 so as to be movable in the direction of an arrow C.

Since the radiography apparatus 1 according to this embodiment has theabove-mentioned configuration, the subject H who lies in a supineposition on the imaging table 40 is irradiated with radiation from thelower side of the subject H and the radiation detector 5 of the imagingunit 3 detects the radiation transmitted through the subject H toacquire a radiographic image of the subject H. Here, the C-arm 2 ismovable in the direction of the arrow A, the direction of the arrow B,and the direction of the arrow C and the radiography apparatus 1 ismovable by the wheels 11. Therefore, the radiography apparatus 1according to this embodiment can capture an image of a desired part ofthe subject H who lies in a supine position on the imaging table 40 in adesired direction.

The main body unit 10 is provided with an interface (I/F) unit 13, theimaging control unit 14, and a positional information acquisition device15 according to this embodiment.

The I/F unit 13 has a function of performing wireless or wiredcommunication with an external apparatus and a console that controls theoverall operation related to the capture of a radiographic image by theradiography apparatus 1 (which are not illustrated). The radiographyapparatus 1 according to this embodiment captures an image of thesubject H on the basis of an imaging command received from the consolethrough the I/F unit 13.

The imaging control unit 14 directs the first and second radiationsources 6A and 6B of the radiation emitting unit 4 to emit the first andsecond radiations R1 and R2 on the basis of the imaging conditionsassociated with an imaging command from the console, respectively. Inaddition, the imaging control unit 14 directs the radiation detector 5of the imaging unit 3 to detect the first and second radiations R1 andR2 transmitted through the subject H according to the timing when thefirst and second radiations R1 and R2 are emitted from the first andsecond radiation sources 6A and 6B, respectively, and generates firstand second radiographic images G1 and G2 of the subject H. The generatedfirst and second radiographic images G1 and G2 are output to the mainbody unit 10. The timing when the first and second radiations R1 and R2are emitted from the first and second radiation sources 6A and 6B,respectively, and the timing when the radiation detector 5 detects thefirst and second radiations R1 and R2 will be described below.

In addition, a user interface 16 is provided above the main body unit10. The user interface 16 has a function by which a user, such as atechnician or a doctor who takes a radiographic image using theradiography apparatus 1, inputs a command related to the capture of aradiographic image, a function which displays a radiographic imageacquired by imaging as a radioscopic image, and a function whichprovides information related to the capture of a radiographic image tothe user. A touch panel display is given an example of the userinterface 16.

Next, the positional information acquisition device according to thisembodiment will be described. FIG. 3 is a diagram schematicallyillustrating the configuration of the positional information acquisitiondevice according to this embodiment. As illustrated in FIG. 3, thepositional information acquisition device 15 is a computer and comprisesa central processing unit (CPU) 21, a memory 22, and a storage 23 as theconfiguration of a standard computer.

A positional information acquisition program according to thisembodiment is installed in the positional information acquisition device15 according to this embodiment. The positional information acquisitionprogram is stored in a storage device of a server computer connected tothe network or a network storage such that it can be accessed from theoutside, is downloaded to the positional information acquisition device15 through the I/F unit 13 on demand, and is installed in the positionalinformation acquisition device 15. Alternatively, the positionalinformation acquisition program is recorded on a recording medium, suchas a digital versatile disc (DVD) or a compact disc read only memory(CD-ROM), is distributed, and is installed in the positional informationacquisition device 15 from the recording medium.

The storage 23 is a storage device, such as a hard disk drive or a solidstate drive (SSD), and stores various kinds of information including thepositional information acquisition program. The radiographic imageacquired by imaging is also stored in the storage 23.

For example, the programs stored in the storage 23 are temporarilystored in the memory 22 in order to cause the CPU 21 to perform variousprocesses. The positional information acquisition program defines, asprocesses performed by the CPU 21, an image acquisition process thatacquires a radiographic image set including the first and secondradiographic images G1 and G2 acquired by the radiography apparatus 1 ata predetermined time interval, a feature point detection process thatdetects at least one common feature point in the subject H from each ofthe first and second radiographic images G1 and G2 included in theradiographic image set, a positional information derivation process thatderives three-dimensional positional information of at least one featurepoint in the subject H, using a positional relationship between theposition of the feature point detected from the first and secondradiographic images G1 and G2 on the detection surface 5A of theradiation detector 5 and the positions of the first and second radiationsources 6A and 6B, a three-dimensional information derivation processthat derives three-dimensional information related to a target structurein the subject H, and a display control process that displays positionalinformation on the user interface 16 as described below.

Then, the CPU 21 performs these processes according to the positionalinformation acquisition program such that the computer functions as thepositional information acquisition device 15 comprising an imageacquisition unit 31, a feature point detection unit 32, a positionalinformation derivation unit 33, a three-dimensional informationderivation unit 34, and a display control unit 35.

The image acquisition unit 31 acquires a radiographic image setincluding the first and second radiographic images G1 and G2 of thesubject H generated by the control of the imaging control unit 14 forthe first and second radiation sources 6A and 6B and the radiationdetector 5. Next, the timing when the first and second radiation sources6A and 6B emit the first and second radiations R1 and R2 and the timingwhen the radiation detector 5 detects the first and second radiations R1and R2 will be described. FIG. 4 is a diagram illustrating the timingwhen the first and second radiation sources 6A and 6B emit the first andsecond radiations R1 and R2 and the timing when the radiation detector 5detects the first and second radiations R1 and R2.

FIG. 4 illustrates a timing T1 when the first radiation source 6A emitsthe first radiation R1, a timing T2 when the second radiation source 6Bemits the second radiation R2, and a timing T3 when the radiationdetector 5 detects the first and second radiations R1 and R2. Inaddition, T4 is a positional information derivation timing which will bedescribed below.

As illustrated in FIG. 4, in a case in which the first radiation R1 isemitted from the first radiation source 6A, the radiation detector 5detects the first radiation R1 transmitted through the subject H andgenerates the first radiographic image G1. In a case in which theradiation detector 5 generates the first radiographic image G1, thesecond radiation source 6B emits the second radiation R2 and theradiation detector 5 detects the second radiation R2 transmitted throughthe subject H and generates the second radiographic image G2. In a casein which the radiation detector 5 generates the second radiographicimage G2, the first radiation source 6A emits the next first radiationR1 and the radiation detector 5 detects the next first radiation R1transmitted through the subject H and generates the next firstradiographic image G1. This is repeated to alternately and repeatedlyacquire the first radiographic image G1 and the second radiographicimage G2. The image acquisition unit 31 acquires the first and secondradiographic images G1 and G2 that are temporally adjacent to each otheras the radiographic image set.

The time interval at which the radiation detector 5 generates the firstand second radiographic images G1 and G2 is 25 to 60 fps, for example,30 fps. In a case in which the time interval at which the first andsecond radiographic images G1 and G2 are generated is 30 fps, the timingwhen the first and second radiations R1 and R2 are emitted from thefirst and second radiation sources 6A and 6B, respectively, is 15 fps.

Here, a medical procedure in a case in which a catheter treatment isperformed for the abdominal aneurysm of the subject H using theradiography apparatus 1 according to this embodiment will be described.FIG. 5 is a diagram illustrating a radioscopic image displayed on theuser interface 16 in a case in which a catheter treatment is performed.As illustrated in FIG. 5, in a case in which a catheter treatment forthe abdominal aneurysm is performed, a bifurcated stent 51 inserted intoa guide wire 52 is inserted into the aorta 50 from the artery in onegroin and one branch 51A of the stent 51 is expanded by the guide wire52. Then, an operation is performed which inserts another guide wire 53into the aorta 50 from the artery in the other groin and passes theguide wire 53 through the other branch 51B of the stent 51 to expand thebranch 51B of the stent 51. In this case, in this embodiment, the firstradiographic image G1 or the second radiographic image G2 of theabdominal aneurysm of the subject H is displayed as a radioscopic imageof the moving image on the user interface 16. The user performs anoperation of passing the guide wire 53 through the branch 51B of thestent 51 while viewing the radioscopic image displayed on the userinterface 16.

Here, the diameter of the branch 51B of the stent 51 is small and theradioscopic image displayed on the user interface 16 is atwo-dimensional image. Therefore, it is difficult to know athree-dimensional positional relationship between an end portion of thebranch 51B of the stent 51 and a leading end 53A of the guide wire 53.For example, in the radioscopic image illustrated in FIG. 5, the guidewire 53 seems to be inserted into the branch 51B of the stent 51.However, in practice, as illustrated in FIG. 6, there is a possibilitythat the guide wire 53 will not be inserted into the branch 51B.

Further, in a case in which lumbar spine fusion is performed, aradiographic image of the front of the subject H is captured, a screwinsertion position is determined, a radioscopic image of the side of thesubject H illustrated in FIG. 7 is displayed as a moving image, and ascrew 55 is inserted into the lumbar spine 56 while a depth and an angleare checked. However, since the radioscopic image is a two-dimensionalimage, it is difficult to know the insertion position and insertionangle of the screw 55 and erroneous insertion is likely to occur. Thisembodiment has been made in order to solve these problems.

The feature point detection unit 32 detects at least one common featurepoint in the subject H from each of the first and second radiographicimages G1 and G2 included in the radiographic image set. For example, inthe case of the catheter treatment, the leading end 53A of the guidewire 53 included in each of the first and second radiographic images G1and G2 is detected as the feature point. In the case of the lumbar spinefusion, a leading end 55A and a rear end 55B of the screw 55 included ineach of the first and second radiographic images G1 and G2 are detectedas the feature points. In this embodiment, the feature point detectionunit 32 has a learned model which has been trained so as to detect thefeature points in the first and second radiographic images G1 and G2.

The feature point includes not only one pixel but also a region having acertain area formed by a plurality of pixels. For example, the leadingend 53A of the guide wire 53, the leading end 55A of the screw 55, andthe rear end 55B of the screw 55 have a certain area and are included inthe feature points in this embodiment.

The learned model is a neural network that has been subjected todeep-learning so as to detect the feature points included in the firstand second radiographic images G1 and G2. The learned model is generatedby training a neural network using a large number of images, in whichfeature points have been known, as training data. Therefore, in a casein which the first and second radiographic images G1 and G2 are input,the feature point detection unit 32 detects a common feature point fromthe first and second radiographic images G1 and G2 and outputs thetwo-dimensional position coordinates of the detected feature point.

The learned model may be, for example, a support vector machine (SVM), aconvolutional neural network (CNN), and a recurrent neural network (RNN)in addition to the neural network subjected to deep learning.

In this embodiment, the feature point detection unit 32 detects thefeature points using the learned model. However, the invention is notlimited thereto. For example, any method, such as a method for detectingthe feature points included in the first and second radiographic imagesG1 and G2 using template matching, may be used as a method for detectingthe feature points.

The positional information derivation unit 33 derives thethree-dimensional positional information of the feature point in thesubject H, using the positional relationship between the position of thefeature point detected from the first and second radiographic images G1and G2 on the detection surface 5A of the radiation detector 5 and thepositions of the first and second radiation sources 6A and 6B. FIG. 8 isa diagram illustrating the derivation of the three-dimensionalpositional information of the feature point. The positional informationderivation unit 33 acquires the information of a radiation sourceposition S1 (sx1, sy1, sz1) of the first radiation source 6A, aradiation source position S2 (sx2, sy2, sz2) of the second radiationsource 6B, a position D1 (dx1, dy1, dz1) of the feature point detectedin the first radiographic image G1, and a position D2 (dx2, dy2, dz2) ofthe feature point detected in the second radiographic image G2illustrated in FIG. 8.

In a case in which a coordinate system having, as the origin, anyposition on the C-arm 2 of the radiography apparatus 1 is set, thethree-dimensional coordinates (sx1, sy1, sz1) of the radiation sourceposition S1 and the three-dimensional coordinates (sx2, sy2, sz2) of theradiation source position S2 can be derived on the basis of thepositional relationship between the origin and the first and secondradiation sources 6A and 6B. For example, in this embodiment, acoordinate system having, as the origin, a point that bisects a lineconnecting the centers of the first and second emission portions 4A and4B of the radiation emitting unit 4 can be set.

Since the SID is known, it is possible to derive the three-dimensionalcoordinates of the center position of the detection surface 5A of theradiation detector 5 with respect to the origin. In addition, it ispossible to derive the three-dimensional coordinates of the positions D1and D2 of the feature points from the two-dimensional positioncoordinates of the feature points in the first and second radiographicimages G1 and G2 detected by the feature point detection unit 32, usingthe three-dimensional coordinates of the center position of thedetection surface 5A of the radiation detector 5.

The positional information derivation unit 33 sets a straight line L1connecting the radiation source position S1 and the position D1 of thefeature point and a straight line L2 connecting the radiation sourceposition S2 and the position D2 of the feature point. Any point P1 onthe straight line L1 and any point P2 on the straight line L2 areexpressed by the following Expression (1) using the radiation sourcepositions S1 and S2 and the positions D1 and D2 of the feature points.In Expression (1), t and s are parameters.

P1=(1−t)·S1+t·D1

P2=(1−s)·S2+s·D2   (1)

Ideally, the feature point in the subject H detected in the first andsecond radiographic images G1 and G2 is located at an intersection pointbetween the point P1 on the straight line L1 and the point P2 on thestraight line L2 in a three-dimensional space. Therefore, in thisembodiment, the positional information derivation unit 33 derives thethree-dimensional coordinates of a point, at which the distance betweenthe point P1 and the point P2 is the minimum, as three-dimensionalpositional information P0(x0, y0, z0) of the feature point detected inthe first and second radiographic images G1 and G2, using the followingExpression (2).

P0=min(P1−P2)²   (2)

In a case in which the image acquisition unit 31 acquires a radiographicimage set including the first and second radiographic images G1 and G2at successive timings, the positional information derivation unit 33derives the positional information P0 using the first and secondradiographic images G1 and G2 included in the acquired radiographicimage set. Therefore, the timing when the positional informationderivation unit 33 derives the positional information P0 is a timing T4illustrated in FIG. 4.

The three-dimensional information derivation unit 34 captures the imagesof the subject H in two directions and derives three-dimensionalinformation related to a target structure which is a target included inthe subject H during a medical procedure. For example, in the case of acatheter treatment for the abdominal aneurysm, first, an operation isperformed which expands the branch 51A after the stent 51 is insertedand inserts the guide wire 53 into the branch 51B. Therefore, thethree-dimensional information derivation unit 34 derives the centerposition of the end portion of the branch 51B of the stent 51 as thethree-dimensional information related to the target structure. FIG. 9 isa diagram illustrating the capture of the images of the subject H in twodirections and FIG. 10 is a diagram illustrating radiographic imagesacquired by the imaging in two directions.

The C-arm 2 is moved in the state illustrated in FIG. 1 and the imagingcontrol unit 14 irradiates the subject H with radiation in the directionof an arrow E1 illustrated in FIG. 9 to acquire a radiographic image GE1illustrated in FIG. 10 in response to a command from the user. Inaddition, the radiation emitting unit 4 is moved to the right side ofthe subject H in FIG. 1 and the subject H is irradiated with radiationin the direction of an arrow E2 to acquire a radiographic image GE2illustrated in FIG. 10. The radiographic images GE1 and GE2 include theimage of the stent 51. The coordinates of the center positions of theradiographic images GE1 and GE2 are known since they are matched withthe coordinates of the center position of the detection surface 5A ofthe radiation detector 5. Therefore, the three-dimensional informationderivation unit 34 derives the three-dimensional coordinates of thecenter position of the end portion of the branch 51B, into which theguide wire for the stent 51 is to be inserted, in the radiographicimages GE1 and GE2 as the three-dimensional information of the targetstructure in the same coordinate system as that in a case in which thefeature point is detected.

Here, the coordinate system is not limited to the same coordinate systemas that in a case in which the feature point is detected. For example, acoordinate system having the center position of the end portion of thebranch 51B of the stent 51 as the origin may be set.

In addition, the three-dimensional information derivation unit 34 maydirect the radiography apparatus 1 to perform tomosynthesis imaging togenerate a three-dimensional image of a target part of the subject H andmay derive the three-dimensional information of a target structure fromthe three-dimensional image acquired by the tomosynthesis imaging.

In the tomosynthesis imaging, while the C-arm 2 is being rotated in thedirection of the arrow A, one (here, the first radiation source 6A) ofthe first and second radiation sources 6A and 6B emits radiation at aplurality of radiation source positions to capture the images of thesubject H, thereby acquiring a plurality of projection images. Then, thethree-dimensional information derivation unit 34 reconstructs theplurality of projection images using a back projection method, such as asimple back projection method or a filtered back projection method, togenerate tomographic images in a plurality of tomographic planes of thesubject H. Then, a three-dimensional image formed by the plurality oftomographic images is generated.

The three-dimensional information derivation unit 34 performs coordinatetransform such that the coordinate system of the three-dimensional imageis matched with the coordinate system of the feature point and derivesthe three-dimensional coordinates of the center position of the endportion of the branch 51B of the stent 51 as the three-dimensionalinformation of the target structure. In this case, a coordinate systemhaving the center position of the end portion of the branch 51B of thestent 51 as the origin may be set.

In addition, the three-dimensional information derivation unit 34 mayderive three-dimensional information from a three-dimensional imagewhich has been acquired in advance by, for example a computed tomography(CT) apparatus or a magnetic resonance imaging (MRI) apparatus. In thiscase, similarly to the three-dimensional image acquired by thetomosynthesis imaging, the three-dimensional information derivation unit34 may perform coordinate transform such that the coordinate system ofthe three-dimensional image which has been acquired in advance ismatched with the coordinate system of the feature point and may derivethe three-dimensional coordinates of the center position of the endportion of the branch 51B of the stent 51 as the three-dimensionalinformation of the target structure. In this case, a coordinate systemhaving the center position of the end portion of the branch 51B of thestent 51 as the origin may be set.

In contrast, in a case in which lumbar spine fusion is performed, thethree-dimensional information derivation unit 34 derives, as thethree-dimensional information of the target structure, thethree-dimensional coordinates of an insertion position and an arrivalposition in the lumbar spine which has been specified in advance in thethree-dimensional image of the subject H acquired by the CT apparatus orthe MRI apparatus before a medical procedure. In this case, thethree-dimensional information derivation unit 34 generates projectionimages GP1 and GP2 obtained by projecting the three-dimensional image inthe direction of the arrow El and the direction of the arrow E2illustrated in FIG. 9, respectively. FIG. 11 is a diagram illustratingthe projection images in two directions. As illustrated in FIG. 11, theprojection image GP1 is a front view of the lumbar spine of the subjectH and the projection image GP2 is a side view of the lumbar spine of thesubject H. Here, the insertion position and the arrival position of thescrew 55 are predetermined and set on the three-dimensional image by anexamination before a medical procedure. Therefore, an insertion positionPS and an arrival position PE are specified in the projection images GP1and GP2.

In addition, the three-dimensional information derivation unit 34captures the images of the subject H in the two directions illustratedin FIG. 9 and acquires radiographic images GE11 and GE12 illustrated inFIG. 12. Then, the three-dimensional information derivation unit 34matches the coordinate system of the radiographic images GE11 and GE12with the coordinate system of the projection images GP1 and GP2 andspecifies an insertion position PS1 and an arrival position PE1 in theradiographic images GE11 and GE12. In this case, it is preferable thatthe coordinate systems to be matched with each other have the insertionposition PS in the projection images GP1 and GP2 as the origin. However,the invention is not limited thereto. The coordinate system of theradiographic images GE11 and GE12 may be matched with a coordinatesystem having any point on the projection images GP1 and GP2 as theorigin or the coordinate system of the projection images GP1 and GP2 maybe matched with the coordinate system of the radiographic images GE11and GE12.

The display control unit 35 displays the positional information P0 onthe user interface 16. In this case, the display control unit 35displays the positional information P0 using the three-dimensionalinformation of the target structure derived by the three-dimensionalinformation derivation unit 34. FIG. 13 is a diagram illustrating apositional information screen in a case in which a catheter treatment isperformed. As illustrated in FIG. 13, a positional information screen 60has a radioscopic image display region 61 and a display region 62 forthe positional information P0. The first radiographic image G1 issequentially displayed as a radioscopic image in the display region 61.Therefore, the radioscopic images are displayed as a moving image in thedisplay region 61. In addition, the second radiographic image G2 may besequentially displayed as the radioscopic image in the display region61.

Here, the three-dimensional information derivation unit 34 derives thethree-dimensional coordinates of the center position of the branch 51Bof the stent 51 as the three-dimensional information of the targetstructure and the positional information derivation unit 33 derives thepositional information P0 of the leading end 53A of the guide wire 53.In addition, the diameter of the branch 51B of the stent 51 is known.Therefore, the display control unit 35 generates a stent image GT0schematically indicating the shape of the branch 51B of the stent 51 anddisplays the stent image GT0 in the positional information displayregion 62. The stent image GT0 is an image as the end portion of thebranch 51B of the stent 51 is viewed from the direction of the centralaxis. Further, the display control unit 35 displays a mark M0 indicatingthe position of the leading end 53A of the guide wire 53 in the displayregion 62. In this case, the display control unit 35 matches thepositional relationship between the mark M0 and the stent image GT0 withthe positional relationship between the leading end 53A of the guidewire 53 and the center position of the branch 51B of the stent 51derived by the three-dimensional information derivation unit 34. Here,the position of the leading end 53A of the guide wire 53 is acquired inthree-dimensional coordinates. Therefore, the mark M0 indicates theposition of the leading end 53A of the guide wire 53 in the image inwhich the branch 51B of the stent 51 is viewed from the direction of thecentral axis.

The user performs an operation of inserting the guide wire 53 into thebody of the subject H while viewing the positional information screen 60such that the mark M0 is located in a circle indicating the end portionof the branch 51B in the stent image GT0. Here, the positionalrelationship between the stent image GT0 and the mark M0 illustrated inFIG. 13 indicates that the leading end 53A of the guide wire 53 isseparated from the end portion of the branch 51B of the stent 51. Whileviewing the positional information screen 60, the user can adjust theposition of the guide wire 53 inserted into the subject H such that themark M0 is located in the stent image GT0. Therefore, it is possible toreduce errors in the insertion of the guide wire 53 into the stent 51 asillustrated in FIG. 6.

The display control unit 35 may notify that the guide wire 53 hasreached the center position of the branch 51B of the stent 51 and hasbeen inserted into the branch 51B through the user interface 16. Thenotification may be performed by text display or sound. Further, bothdisplay and sound may be used for the notification.

Further, the sound may be changed according to the distance between theleading end 53A of the guide wire 53 and the center position of thebranch 51B. For example, a beep sound may be intermittently output asthe sound and the interval between the beep sounds may become shorter asthe leading end 53A of the guide wire 53 becomes closer to the centerposition of the branch 51B. In addition, the sound may be changed in acase in which the leading end 53A of the guide wire 53 is inserted intothe branch 51B.

In a case in which the leading end 53A of the guide wire 53 passesthrough the end portion of the branch 51B without being inserted intothe branch 51B or the leading end 53A of the guide wire 53 is separatedfrom the center of the branch 51B by a predetermined threshold value ormore, a warning indicating the fact may be issued through the userinterface 16.

FIG. 14 illustrates a positional information screen in a case in whichlumbar spine fusion is performed. As illustrated in FIG. 14, apositional information screen 70 has a radioscopic image display region71 and a positional information display region 72. The firstradiographic image G1 obtained by capturing the image of the lumbarspine from the side is sequentially displayed in the display region 71.Therefore, the radioscopic images are displayed as a moving image in thedisplay region 71. The first radiographic image G1 includes an image ofthe screw 55. Further, the second radiographic image G2 may besequentially displayed as a radioscopic image in the display region 71.

Here, the three-dimensional information derivation unit 34 derives thethree-dimensional coordinates of the insertion position PS and thearrival position PE of the screw 55 in the lumbar spine as thethree-dimensional information of the target structure. The positionalinformation derivation unit 33 derives the positional information P0 ofthe leading end 55A and the rear end 55B of the screw 55. Therefore, thedisplay control unit 35 generates a tomographic image GD0 of the lumbarspine into which the screw 55 is inserted, using the three-dimensionalimage of the subject H which has been acquired in advance, and displaysthe generated tomographic image GD0 in the positional informationdisplay region 72. The tomographic image GD0 of the lumbar spinedisplayed in the display region 72 indicates an axial cross section.

The display control unit 35 displays a mark M1 obtained by projectingthe screw 55 derived by the positional information derivation unit 33onto the tomographic plane of the tomographic image GD0 in thepositional information display region 72. In this case, the displaycontrol unit 35 matches the positional relationship between the leadingend and the rear end of the mark M1 and the insertion position PS andthe arrival position PE on the tomographic image GD0 with the positionalrelationship between the leading end 55A and the rear end 55B of thescrew 55 and the insertion position PS and the arrival position PEderived by the three-dimensional information derivation unit 34.Further, the display control unit 35 displays the remaining distancefrom the leading end 55A of the screw 55 to the insertion position PSderived by the positional information derivation unit 33 in aninformation display region 74 until the screw 55 reaches the insertionposition PS. In this embodiment, since the coordinate system having theinsertion position PS as the origin is also set for the radiographicimages G1 and G2, it is possible to derive the distance from the currentposition of the leading end 55A of the screw 55 from the origin as theremaining distance from the leading end 55A of the screw 55 to theinsertion position PS.

Further, the display control unit 35 derives an angle (referred to as afirst angle) of the axis of the screw 55 with respect to the axial crosssection from the positions of the leading end 55A and the rear end 55Bof the screw 55 derived by the positional information derivation unit33. In addition, an angle (referred to as a second angle) at which thescrew 55 is to be inserted is derived from the insertion position PS andthe arrival position PE derived by the three-dimensional informationderivation unit 34. Then, the difference of the first angle from thesecond angle is derived and the derived angle is displayed in theinformation display region 74. In FIG. 14, a remaining distance of 10 mmand an angle of 0 degrees are displayed. The angle of 0 degreesindicates that the angle at which the screw 55 is inserted is matchedwith the angle formed by the insertion position PS and the arrivalposition PE. After the screw 55 is inserted into the lumbar spine fromthe insertion position PS, the remaining distance from the leading end55A of the screw 55 to the arrival position PE may be displayed in theinformation display region 74.

The display control unit 35 may issue a warning in a case in which theleading end 55A of the screw 55 is at a position that is separated fromthe insertion position PS by a predetermined threshold value or more.Further, in a case in which the angle of the screw 55 is greater than apredetermined threshold value (for example, 10 degrees), the displaycontrol unit 35 may issue a warning.

The user can insert the screw 55 into the body of the subject H suchthat the screw 55 is inserted into the lumbar spine from the insertionposition PS while viewing the display of the tomographic image GD0, themark M1, and the information display region 74. In addition, the usercan insert the screw 55 into the lumbar spine of the subject H such thatthe inserted screw 55 correctly reaches the arrival position PE.

Even in the case of lumbar spine fusion, the display control unit 35 maynotify that the leading end 55A of the screw 55 has reached theinsertion position PS and the leading end 55A of the screw 55 hasreached the arrival position PE through the user interface 16. Inaddition, the notification may be performed in a case in which the angleof the screw 55 is matched with the angle at which the screw 55 is to beinserted. The notification may be performed by text display or sound.Further, both display and sound may be used.

Further, the sound may be changed according to the distance between theleading end 55A of the screw 55 and the insertion position PS and thearrival position PE. For example, a beep sound may be intermittentlyoutput as the sound and the interval between the beep sounds may becomeshorter as the leading end 55A of the screw 55 becomes closer to theinsertion position PS and the arrival position PE. In addition, thesound may be changed in a case in which the leading end 55A of the screw55 reaches the insertion position PS and the arrival position PE.

Next, a process performed in this embodiment will be described. FIG. 15is a flowchart illustrating the process performed in this embodiment. Itis assumed that the three-dimensional information of a target structurehas been derived in advance by the three-dimensional informationderivation unit 34 and then stored in the storage 23.

The user inputs an imaging start command through the user interface 16to start the process and the image acquisition unit 31 acquires a set ofthe first radiographic image G1 and the second radiographic image G2(the acquisition of a radiographic image set; Step ST1). In a case inwhich the set of the first radiographic image G1 and the secondradiographic image G2 is acquired, the feature point detection unit 32detects at least one common feature point from the first and secondradiographic images G1 and G2 (Step ST2). Then, the positionalinformation derivation unit 33 derives the three-dimensional positionalinformation of at least one feature point in the subject H, using thepositional relationship between the position of at least one featurepoint detected from each of the first and second radiographic images G1and G2 on the detection surface 5A of the radiation detector 5 and thepositions of the first and second radiation sources 6A and 6B (StepST3).

The display control unit 35 displays a positional information screen onthe user interface 16 (Step ST4). The process returns to Step ST1. Theprocess from Step ST1 to Step ST4 is repeatedly performed until aprocess end command is issued.

As such, in this embodiment, at least one common feature point in thesubject H is detected from each of the first and second radiographicimages G1 and G2 and the three-dimensional positional information of atleast one feature point in the subject H is derived using the positionalrelationship between the position of at least one feature point detectedfrom each of the first and second radiographic images G1 and G2 on thedetection surface 5A of the radiation detector 5 and the positions ofthe first and second radiation sources 6A and 6B. Therefore, it ispossible to acquire the three-dimensional positional information of afeature point, using a smaller amount of calculation as that in a casein which a three-dimensional image is generated from a plurality ofradiographic images. As a result, according to this embodiment, it ispossible to understand the three-dimensional position of a featurepoint, such as a surgical instrument, in the subject H in real time.

In the above-described embodiment, the first radiographic image G1 andthe second radiographic image G2 are alternately acquired. However, theinvention is not limited thereto. As illustrated in FIG. 16, one secondradiographic image G2 may be acquired for every several frames of thefirst radiographic images G1. In FIG. 16, the second radiographic imageG2 is acquired once while four frames of the first radiographic imagesG1 are acquired. In this case, the derivation of the positionalinformation is performed once while four frames of the firstradiographic images G1 are acquired.

In the above-described embodiment, in a case in which a cathetertreatment is performed, the three-dimensional information derivationunit 34 derives the center position of the branch 51B of the stent 51 asthe three-dimensional information of the target structure. However, theinvention is not limited thereto. The feature point detection unit 32may detect the center position of the branch 51B of the stent 51 as afeature point different from the leading end 53A of the guide wire 53from the first and second radiographic images G1 and G2 and thepositional information derivation unit 33 may derive the positionalinformation of the center position of the branch 51B.

In the above-described embodiment, radiation is not particularly limitedand rays other than X-rays, such as a-rays or y-rays, may be applied.

In the above-described embodiment, in a case in which a cathetertreatment and lumbar spine fusion are performed, the positionalinformation acquisition device and the radiography apparatus accordingto the present disclosure are applied. However, the invention is notlimited thereto. The present disclosure may be applied to any medicalprocedure using a radioscopic image.

In the above-described embodiment, the first and second radiationsources 6A and 6B are arranged in the y-axis direction illustrated inFIG. 1 in the radiation emitting unit 4. However, the first and secondradiation sources 6A and 6B may be arranged in the x-axis direction.

In the above-described embodiment, the radiation emitting unit 4includes the two radiation sources 6A and 6B. However, the invention isnot limited thereto. The radiation emitting unit 4 may include three ormore radiation sources. In this case, the positional information may bederived using a plurality of radiographic images acquired by irradiatingthe subject H with radiation emitted from three or more radiationsources. Specifically, the positional information may be derived using acombination of two radiographic images generated by radiation emittedfrom two radiation sources among three or more radiation sources.

In the above-described embodiment, for example, the following variousprocessors can be used as the hardware structure of processing unitsperforming various processes, such as the image acquisition unit 31, thefeature point detection unit 32, the positional information derivationunit 33, the three-dimensional information derivation unit 34, and thedisplay control unit 35. The various processors include a CPU which is ageneral-purpose processor executing software (program) to function asvarious processing units, a programmable logic device (PLD), such as afield programmable gate array (FPGA), which is a processor whose circuitconfiguration can be changed after manufacture, and a dedicated electriccircuit, such as an application specific integrated circuit (ASIC),which is a processor having a dedicated circuit configuration designedto perform a specific process.

One processing unit may be configured by one of the various processorsor a combination of two or more processors of the same type or differenttypes (for example, a combination of a plurality of FPGAs or acombination of a CPU and an FPGA). In addition, a plurality ofprocessing units may be configured by one processor.

A first example of the configuration in which a plurality of processingunits are configured by one processor is an aspect in which oneprocessor is configured by a combination of one or more CPUs andsoftware and functions as a plurality of processing units. Arepresentative example of this aspect is a client computer or a servercomputer. A second example of the configuration is an aspect in which aprocessor that implements the functions of the entire system including aplurality of processing units using one integrated circuit (IC) chip isused. A representative example of this aspect is a system-on-chip (SoC).As such, various processing units are configured by using one or more ofthe various processors as a hardware structure.

In addition, specifically, an electric circuit (circuitry) obtained bycombining circuit elements, such as semiconductor elements, can be usedas the hardware structure of the various processors.

What is claimed is:
 1. A positional information acquisition devicecomprising: at least one processor configured to: acquire a radiographicimage set including a plurality of radiographic images, which have beengenerated by alternately irradiating a subject with radiation emittedfrom a plurality of radiation sources provided at different positionsand alternately detecting the radiation transmitted through the subjectusing one detection unit, at a predetermined time interval; detect atleast one common feature point in the subject from each of the pluralityof radiographic images included in the radiographic image set; andderive three-dimensional positional information of the at least onefeature point in the subject using a positional relationship between aposition of the at least one feature point detected from each of theplurality of radiographic images on a detection surface of the detectionunit and positions of the plurality of radiation sources.
 2. Thepositional information acquisition device according to claim 1, furthercomprising: wherein the processor is further configured to display thepositional information on a display unit.
 3. The positional informationacquisition device according to claim 1, wherein the processor isfurther configured to detect a point on a surgical instrument insertedinto the subject as the feature point.
 4. A radiography apparatuscomprising: a plurality of radiation sources that are provided at apredetermined interval; the positional information display deviceaccording to claim 1; and at least one processor configured to face theplurality of radiation sources, detect radiation which has been emittedfrom each of the plurality of radiation sources and transmitted througha subject, generate a radiographic image of the subject, and generate aradiographic image set including a plurality of radiographic images at apredetermined time interval by controlling a timing when each of theplurality of radiation sources emits the radiation and a timing when thedetection unit detects the radiation transmitted through the subjectsuch that the plurality of radiation sources alternately irradiate thesubject with the radiation and the detection unit alternately detectsthe radiation transmitted through the subject.
 5. The radiographyapparatus according to claim 4, wherein the number of radiation sourcesis
 2. 6. The radiography apparatus according to claim 5, wherein theprocessor is further configured to direct one of the two radiationsources to sequentially emit radiation at a first time interval, directsthe other radiation source to sequentially emit radiation at a secondtime interval equal to or longer than the first time interval, andcontrols the detection unit so as to detect the radiation at all timingswhen the two radiation sources emit the radiation, and acquire, as theradiographic image set, two radiographic images generated by detectingtwo temporally adjacent radiations which have been emitted from the tworadiation sources using the detection unit.
 7. A positional informationacquisition method comprising: acquiring a radiographic image setincluding a plurality of radiographic images, which have been generatedby alternately irradiating a subject with radiation emitted from aplurality of radiation sources provided at different positions andalternately detecting the radiation transmitted through the subjectusing one detection unit, at a predetermined time interval; detecting atleast one common feature point in the subject from each of the pluralityof radiographic images included in the radiographic image set; andderiving three-dimensional positional information of the at least onefeature point in the subject using a positional relationship between aposition of the at least one feature point detected from each of theplurality of radiographic images on a detection surface of the detectionunit and positions of the plurality of radiation sources.
 8. Anon-transitory computer-readable storage medium that stores a positionalinformation acquisition program that causes a computer to perform: astep of acquiring a radiographic image set including a plurality ofradiographic images, which have been generated by alternatelyirradiating a subject with radiation emitted from a plurality ofradiation sources provided at different positions and alternatelydetecting the radiation transmitted through the subject using onedetection unit, at a predetermined time interval; a step of detecting atleast one common feature point in the subject from each of the pluralityof radiographic images included in the radiographic image set; and astep of deriving three-dimensional positional information of the atleast one feature point in the subject using a positional relationshipbetween a position of the at least one feature point detected from eachof the plurality of radiographic images on a detection surface of thedetection unit and positions of the plurality of radiation sources.